Egg yolk shell structure metal organic framework-based halogen-free flame retardant as well as preparation method and application thereof

Abstract

The invention provides a yolk shell structure metal organic framework-based halogen-free flame retardant as well as a preparation method and application thereof, and belongs to the technical field of nano composite flame-retardant materials. The flame retardant is a metal organic framework with a yolk shell structure, and the surface of the metal organic framework with the yolk shell structure is grafted with a ferrocene group and a 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) group; the yolk shell structure comprises an inner core, an outer shell and a cavity located between the inner core and the outer shell. When the flame retardant is applied to epoxy resin, the limit oxygen index of a composite material can reach up to 31.5% only by adding 10 wt% of the flame retardant, the peak heat release rate is reduced by 58.2% when the composite material passes the UL-94 V-0 grade, and release of smoke toxic gas is remarkably inhibited. Meanwhile, the composite material has excellent mechanical properties, the retention rate of tensile strength is greater than 90% (up to 65.4 MPa), and the bending strength is up to 84.2 MPa. According to the invention, halogen-free and low-addition-amount efficient flame retardance and balance of mechanical properties are realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nanocomposite flame-retardant materials, and particularly relates to a metal-organic framework (MOFs) based halogen-free flame retardant with an egg yolk shell structure, a preparation method thereof, and application thereof in polymer materials (particularly epoxy resin). BACKGROUND

[0002] The widespread application of high polymer materials is accompanied by significant fire hazards, and the addition of flame retardants is a key means to improve the fire safety of polymers (such as plastics, rubbers, and textiles). However, the traditional flame-retardant system faces severe challenges: inorganic flame retardants (aluminum hydroxide, magnesium hydroxide, etc.) are environmentally friendly, but require a high filling amount of 30-60 wt% to be effective, which leads to a serious deterioration of the mechanical properties of the material; halogen-based flame retardants are relatively efficient, but release toxic gases such as dioxins and hydrogen halides during combustion, causing environmental and health risks, and have been strictly limited by regulations such as the European Union RoHS; phosphorus-based and nitrogen-based flame retardants have lower toxicity, but still have problems such as poor compatibility with polymers, easy migration and precipitation, and insufficient long-term stability.

[0003] In recent years, metal-organic frameworks (MOFs) have shown potential in the field of flame retardation due to their high specific surface area, adjustable pore size, and rich active sites. However, conventional MOFs flame retardants still have inherent defects: first, the dense structure makes it difficult for the flame-retardant components (metal ions / organic ligands) to be fully released; second, the nanoparticles are prone to agglomeration in the polymer matrix, reducing dispersion and interfacial interaction; third, the thermal stability is insufficient, and the structure collapses easily at high temperatures, affecting the flame-retardant durability. Existing technologies attempt to optimize MOFs by surface modification or composite with other materials, but have not fundamentally solved the contradiction between low active utilization rate and weak structural stability.

[0004] The egg yolk shell structure has potential value in improving the thermal stability of materials and the utilization rate of active components due to its unique configuration. At the same time, researchers have found that a synergistic system can be constructed by combining MOFs with phosphorus-based flame retardants (such as ammonium polyphosphate and hypophosphite), which can significantly improve the efficiency of halogen-free flame retardation: the porous structure of MOFs can adsorb the phosphoric acid source generated by the decomposition of phosphorus-based flame retardants, promoting the formation of a dense carbon layer; the metal nodes (such as Zn 2+ , Co 2+ ) can also catalyze the crosslinking of phosphorus compounds, realizing a gas phase-coagulation phase dual-phase flame retardation mechanism. However, the existing MOFs / phosphorus-based composite system still has obvious limitations: first, the physical mixing of phosphorus-based flame retardants easily covers and blocks the pores on the surface of MOFs, reducing the specific surface area advantage; second, the decomposition of phosphorus-based components and the collapse of MOFs structure are not synchronized at high temperatures, leading to insufficient persistence of the synergistic effect; third, the phosphorus-based flame retardant has strong hygroscopicity, and after being combined with MOFs, it is prone to cause deliquescence and migration, affecting the long-term stability of the material.

[0005] Therefore, developing a new type of flame retardant, which can not only inherit the synergistic flame-retardant effect of MOFs and phosphorus-based components, but also overcome the structural defects and stability bottlenecks of existing composite systems, has become a key problem that the industry urgently needs to break through. SUMMARY

[0006] The purpose of the present application is to solve the problems of the physical blending system of MOFs and phosphorus-based flame retardants, such as the blockage of MOF channels by phosphorus-based components, leading to the loss of high specific surface area and low utilization rate of active sites, poor synergistic flame-retardant persistence (thermal decomposition behavior mismatch between MOFs and phosphorus-based components leading to interruption of the dual-phase flame-retardant mechanism), and long-term stability defects caused by moisture absorption and migration, while breaking through the limitations of traditional halogen-free flame retardants with high additive amount damaging the performance of the matrix, thereby providing a yolk-shell structure metal organic framework-based halogen-free flame retardant and its preparation method and application. By using the space decoupling and cavity confinement strategy, a multi-level active carrier is constructed to achieve efficient loading and thermal release regulation of phosphorus-based flame-retardant components, and the additive amount of the flame retardant is significantly reduced.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: The present application first provides a yolk-shell structure metal organic framework-based halogen-free flame retardant, wherein the flame retardant is a metal organic framework with a yolk-shell structure, and the surface of the yolk-shell structure metal organic framework is grafted with a ferrocene group and a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) group; the yolk-shell structure includes a core, a shell, and a cavity between the core and the shell.

[0008] The present application also provides a preparation method of a yolk-shell structure metal organic framework-based halogen-free flame retardant, which comprises the following steps: Step one: dispersing an aminated metal organic framework material in a solvent to obtain a dispersion liquid; Step two: adding a methanol solution of ferrocene formaldehyde to the dispersion liquid obtained in step one, heating to react, and obtaining a solid; Step three: dispersing the solid obtained in step two in methanol, adding a methanol solution of DOPO, and reacting to obtain a yolk-shell structure metal organic framework-based halogen-free flame retardant.

[0009] Preferably, the aminated metal organic framework material in step one is aminated ZIF-67.

[0010] Preferably, the reaction temperature in step two is 55-65 ℃, and the reaction time is 12-24 h.

[0011] Preferably, the mass ratio of ferrocene formaldehyde to aminated metal organic framework material in step two is 1: (1-2).

[0012] Preferably, the reaction temperature in step three is 55-65 ℃, and the reaction time is 12-24 h.

[0013] Preferably, the mass ratio of the solid to DOPO in step three is 1:2.

[0014] The application further provides application of the above-mentioned egg yolk shell structure metal organic framework based halogen-free flame retardant in epoxy resin.

[0015] Preferably, the application specifically refers to: The ethanol dispersion of the egg yolk shell structure metal organic framework based halogen-free flame retardant, the epoxy resin and the curing agent are stirred and mixed, and then heated for curing to obtain an epoxy resin composite material.

[0016] Preferably, the curing agent is 4,4-diphenyl diphenyl sulfone (DDS), and the type of the epoxy resin is E-44 type epoxy resin.

[0017] Advantages of the application The application provides an egg yolk shell structure metal organic framework based halogen-free flame retardant, a preparation method and application thereof. The flame retardant is a high-efficiency flame retardant system that has both multi-level active carriers and phosphorus-based synergistic functions. The flame retardant provided by the application has a unique egg yolk shell structure. First, ferrocene formaldehyde is reacted with an amino MOF to introduce a ferrocene group, and then reacted with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to graft a DOPO group, forming a FZ@DOPO flame retardant. The flame retardant has a unique "core@cavity@shell" configuration, and the shell has abundant mesoporous channels. On the basis of the inherent micropores of MOFs, a through-hole level is constructed. The unique structure uses the cavity to load the phosphorus component, and the shell constructs the through mesoporous channels, realizing multi-level pore synergism. The presence of the multi-level active carrier significantly improves the adsorption capacity of the polymer pyrolysis macromolecular fragments and smoke toxic gases, and strengthens the condensed phase flame retardation and smoke suppression performance. The phosphorus component loaded in the cavity and the MOF skeleton metal nodes (such as Zn 2+ , Co 2+ ) produce a molecular-level synergistic effect, synchronously catalyze carbonization and capture free radicals, realize gas phase-condensed phase dual-phase efficient flame retardation, and achieve the improvement of the limiting oxygen index under the conditions of halogen-free and low addition amount. In addition, the interface compatibility optimized by the egg yolk shell structure effectively inhibits the migration and deliquescence of the phosphorus-based flame retardant, so that the modified polymer has a tensile strength retention rate of >90% while the bending strength is also improved.

[0018] The experimental results show that when the flame retardant is applied to epoxy resin (such as E-44 type), only 10 wt% of the additive amount is needed, so that the limiting oxygen index of the composite material is as high as 31.5%, the UL-94 V-0 level is passed, the peak heat release rate is reduced by 58.2%, and the release of smoke toxic gas is significantly inhibited (the smoke release rate is reduced by 52.3%, and the CO release rate is reduced by 66.1%). At the same time, the mechanical properties of the composite material are excellent, the tensile strength retention rate is > 90% (reaching 65.4 MPa), and the bending strength reaches 84.2 MPa. The present application realizes efficient flame retardation and mechanical property balance under halogen-free and low additive amount. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a transmission electron microscope image of the halogen-free flame retardant prepared in Example 1; Figure 2 It is a scanning electron microscope image of the halogen-free flame retardant prepared in Example 1; Figure 3 It is an infrared spectrum curve of the halogen-free flame retardant prepared in Example 1; Figure 4 It is an X-ray diffraction curve of the halogen-free flame retardant prepared in Example 1; Figure 5 It is a thermogravimetric curve of the halogen-free flame retardant prepared in Example 1; Figure 6 It is a derivative thermogravimetric curve of the functional flame retardant prepared in Example 1. DETAILED DESCRIPTION

[0020] The present application first provides a yolk-shell structure metal organic framework-based halogen-free flame retardant, the flame retardant is a metal organic framework with a yolk-shell structure, and the metal organic framework with the yolk-shell structure is grafted with a ferrocene group and a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) group; the yolk-shell structure comprises a core, a shell and a cavity between the core and the shell.

[0021] The present application also provides a preparation method of the yolk-shell structure metal organic framework-based halogen-free flame retardant, which comprises the following steps: Step one: disperse the aminated metal organic framework material in a solvent, the solvent is preferably methanol, to obtain a dispersion liquid; the mass g of the aminated metal organic framework material: the volume mL of methanol is 1:100-200; the aminated metal organic framework material is preferably aminated ZIF-67. The preparation method of the aminated ZIF-67 is not limited, and a method known in the art can be used for preparation.

[0022] Step two: add the methanol solution of ferrocene formaldehyde to the dispersion obtained in step one, preferably stir at room temperature first, the stirring time is preferably 1h, then carry out the heating reaction, the heating temperature is preferably 55-65 ℃, the reaction time is preferably 12-24 h, after the reaction is completed, preferably cool to room temperature, centrifugal separation, wash the filter cake with ethanol three times, then dry in an oven at 50-60 ℃ for 12-24 h, to obtain a solid; In the formaldehyde solution of ferrocene formaldehyde, the mass g of ferrocene formaldehyde: the volume mL of methanol is 1:100-200; The mass ratio of ferrocene formaldehyde to the amino-functionalized metal organic framework material in the formaldehyde solution of ferrocene formaldehyde is preferably 1: (1-2); Step three: disperse the solid obtained in step two in methanol, then add the methanol solution of DOPO, preferably stir at room temperature first, the stirring time is preferably 1h, then react at 55-65 ℃ for 12-24 h, after the reaction is completed, cool to room temperature, centrifugal separation, wash the filter cake with ethanol three times, then dry in an oven at 50-60 ℃ for 12-24 h, to obtain a yolk shell structure metal organic framework-based halogen-free flame retardant.

[0023] The mass g of the solid: the volume mL of methanol is 1:100-200; In the methanol solution of DOPO, the mass g of DOPO: the volume mL of methanol is 1:50-100; The mass ratio of the solid to DOPO in the methanol solution of DOPO is 1:2.

[0024] The application also provides the use of the above yolk shell structure metal organic framework-based halogen-free flame retardant in epoxy resin.

[0025] According to the application, the use is specifically: Stir and mix the ethanol dispersion of the yolk shell structure metal organic framework-based halogen-free flame retardant, the epoxy resin and the curing agent, then heat to cure, to obtain an epoxy resin composite material; In the ethanol dispersion of the yolk shell structure metal organic framework-based halogen-free flame retardant, the mass g of the yolk shell structure metal organic framework-based halogen-free flame retardant: the volume mL of ethanol is preferably 5:5-15; The mass ratio of the yolk shell structure metal organic framework-based halogen-free flame retardant, the epoxy resin and the curing agent is preferably 10: (50-100): (25-35); The curing agent is preferably 4,4-diphenyl diphenyl sulfone (DDS); The type of the epoxy resin is preferably E-44 type epoxy resin; The curing temperature is preferably 170-180°C, and the curing time is preferably 3-4h.

[0026] The application will be further described in connection with the following specific examples, in which the raw materials are commercially available.

[0027] Example 1 A preparation method of a yolk-shell structure metal organic framework-based flame retardant, comprising the following steps: S1, preparation of ZIF-67: Take 2.91 g of cobalt nitrate hexahydrate and 3.28 g of 2-methylimidazole and dissolve them in 100 ml of methanol respectively, mix and stir for 1 hour, then stand for 24 hours, centrifugally separate the solid, wash it with methanol three times, and dry it in a 60°C oven for 24 hours to obtain ZIF-67; S2, amination of ZIF-67: Take 0.5 g of ZIF-67 and disperse it in 50 ml of methanol by water bath ultrasonic for 10 minutes, then dissolve 0.5 g of 3,5-diamino-1,2,4-triazole in 50 ml of methanol. Mix the two and stir for 12 hours, centrifugally separate the solid, wash it with methanol three times, and dry it in a 60°C oven for 24 hours to obtain aminated ZIF-67 (NH2-ZIF); S3, aminated ZIF-67 loaded with ferrocene: Take 0.5 g of NH2-ZIF and disperse it in 50 ml of methanol by water bath ultrasonic for 10 minutes, then add 50 ml of methanol solution containing 0.5 g of ferrocene formaldehyde, and stir at room temperature for 1 hour. Next, reflux the mixed solution at 60°C for 24 hours, and then cool it to room temperature. Centrifugally separate the solid, wash it with methanol three times, and dry it in a 60°C oven for 24 hours to obtain aminated ZIF-67 loaded with iron-containing compound composite flame retardant (Fc-ZIF); S4, yolk-shell structure metal organic framework-based flame retardant: Take 0.5 g of Fc-ZIF and disperse it in 50 ml of methanol by water bath ultrasonic for 10 minutes, then add 50 ml of methanol solution containing 1 g of DOPO, and stir at room temperature for 1 hour. Next, reflux the mixed solution at 60°C for 24 hours, and then cool it to room temperature. Centrifugally separate the solid, wash it with methanol three times, and dry it in a 60°C oven for 24 hours to obtain a yolk-shell structure metal organic framework-based flame retardant (FZ@DOPO).

[0028] Figure 1 and Figure 2The images shown are transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of the halogen-free flame retardant obtained in Example 1 of this invention. Observation of both images shows that the material completely retains the typical polyhedral morphology and crystal framework of the original ZIF-67. Furthermore, the TEM images ( Figure 1 It is clearly visible that a unique eggshell structure has formed inside the material; Figure 3 and Figure 4 The infrared spectrum (FT-IR) and X-ray diffraction (XRD) pattern of the product obtained in Example 1 are shown respectively. Figure 3 In the infrared spectrum, characteristic absorption peaks belonging to amino, ferrocene and DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) appeared. Figure 4 The X-ray diffraction pattern showed that the diffraction peak positions were basically consistent with those of the standard card (PDF#89-570) for ZIF-67, with a slight decrease in the number and intensity of peaks, indicating that the amination and loading processes caused some damage to the crystal form but still maintained its main crystal form. These spectral results collectively confirm that the product was obtained by successfully loading ferrocene and DOPO onto ZIF-67 after amination.

[0029] Figure 5 and Figure 6 The thermogravimetric (TG) curves and their corresponding differential thermogravimetric (DTG) curves for the flame retardant obtained in Example 1 are shown below. Figure 5 It can be seen that the residual mass fraction of the material remains at approximately 20% at 800℃. Figure 6 Further data shows that the temperature corresponding to its maximum thermal decomposition rate is above 700°C. These data indicate that the halogen-free flame retardant prepared in this invention has excellent thermal stability.

[0030] Example 2: Application of flame retardants in epoxy resins Weigh 100 g of E-44 epoxy resin into a flask, add 10 ml of ethanol solution containing 10 g of FZ@DOPO, stir at 140 °C for 10 minutes, then add 30 g of 4,4-diphenyl diphenyl sulfone (DDS), stir for 10 minutes, evacuate the mixture for 30 minutes, then transfer it to a preheated polytetrafluoroethylene mold, and cure at 180 °C for 4 hours to obtain an epoxy resin composite material.

[0031] The prepared epoxy resin composite material was tested for flame retardant properties (limiting oxygen index was obtained according to ASTM D 2863 standard; UL-94 rating was obtained according to UL-94 standard, sample size was 125×13×3.2 mm). 3 The cone calorimetry test results were obtained according to ISO 5660, with sample dimensions of 100×100×3 mm.3 , the heat flux is 50 kW / m 2 ). The test results are shown in Table 1: Table 1 Flame-retardant properties of epoxy resin composite

[0032] As can be seen from Table 1, the epoxy resin composite prepared using the functional flame retardant of Example 1 of the present application exhibits excellent flame-retardant and smoke-suppressing properties, and more importantly, it passes the UL-94 test at the V-0 level.

[0033] The prepared epoxy resin composite was subjected to mechanical property testing (the mechanical properties were obtained according to GB / T1040.1-2018 and GB / T9341-2008, wherein the tensile rate was 2 mm / min, the gauge length was 50 mm, the width was 10 mm, the thickness was 3 mm, and the sample was dumbbell-shaped in the tensile test; the sample size was 100x15x4 mm 3 , and the test speed was 2 mm / min in the bending test), and the test results are shown in Table 2: Table 2 Mechanical properties of epoxy resin composite

[0034] As can be seen from Table 2, the epoxy resin composite prepared using the functional flame retardant of Example 1 of the present application has excellent mechanical properties, with a tensile strength close to 70 MPa and a bending strength close to 85 MPa.

[0035] To sum up, the above is only a preferred embodiment of the present application, and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An eggshell structure metal-organic framework based halogen-free flame retardant, characterized in that, The flame retardant is a metal organic framework with a yolk-shell structure, and the yolk-shell structure metal organic framework is surface-grafted with a ferrocene group and a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide group; the yolk-shell structure comprises a core, a shell, and a cavity between the core and the shell.

2. The method for preparing a halogen-free flame retardant based on a yolk shell structure metal-organic framework according to claim 1, characterized in that, The method comprises: Step one: dispersing an aminated metal organic framework material in a solvent to obtain a dispersion liquid; Step two: adding a methanol solution of ferrocene formaldehyde to the dispersion liquid obtained in step one, heating to react, to obtain a solid; Step three: dispersing the solid obtained in step two in methanol, adding a methanol solution of DOPO, and reacting to obtain a yolk-shell structure metal organic framework-based halogen-free flame retardant.

3. The method for preparing a halogen-free flame retardant based on a yolk shell structure metal-organic framework according to claim 2, characterized in that, The aminated metal organic framework material in step one is aminated ZIF-67.

4. The preparation method of a yolk-shell structured metal-organic framework-based halogen-free flame retardant according to claim 2, characterized in that, The reaction temperature in step two is 55-65 ℃, and the reaction time is 12-24 h.

5. The method for preparing a halogen-free flame retardant based on a yolk shell structure metal-organic framework according to claim 2, characterized in that, The mass ratio of ferrocene formaldehyde to the aminated metal organic framework material in step two is 1: (1-2).

6. The method for preparing a halogen-free flame retardant based on a yolk shell structure metal-organic framework according to claim 2, characterized in that, The reaction temperature in step three is 55-65 ℃, and the reaction time is 12-24 h.

7. The method for preparing a halogen-free flame retardant based on a yolk shell structure metal-organic framework according to claim 2, characterized in that, The mass ratio of the solid to DOPO in step three is 1:

2.

8. Use of the yolk-shell structure metal organic framework-based halogen-free flame retardant in claim 1 in an epoxy resin.

9. Use according to claim 8, characterized in that, The use specifically comprises: An ethanol dispersion liquid of the yolk-shell structure metal organic framework-based halogen-free flame retardant, an epoxy resin, and a curing agent are stirred and mixed, then heated for curing to obtain an epoxy resin composite material.

10. Use according to claim 9, characterized in that, The curing agent is 4,4-diphenyl diphenyl sulfone; and the epoxy resin is an E-44 type epoxy resin.

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